We spoke with Jameson Grout, a product specialist in Hubbard Hall's specialty chemical division, about the proper use of black oxide and its features.
Jameson GroutBefore joining Hubbard-Hall, Grout worked up the plating lines, from Lab Technician to Plating Manager and, eventually, Production Manager. In addition to plating, he has experience with aluminum finishing, black oxide, phosphating, nickel, copper, and gold plating, as well as electropolishing and electroless nickel.
Grout holds a Bachelor of Science from Norwich University and CEF-1 Certification through the National Association for Surface Finishing.
Editor-in-Chief Tim Pennington spoke with Grout about the nuances of black oxide:
Tim Pennington: Black oxide does have a fairly dirty and dangerous reputation. I know that some people will say, "I'm not having that in my shop, not going to have it. Too much of a liability," and things such as that. What exactly is black oxide, and whether you feel it deserves that reputation?
Jameson Grout: So visually, it does have a reputation. I mean, we're talking about this supersaturated 285°boiling solution. It's not your typical plating tank. It's murky; it's got scum all over the top. And you see a lot of shops; they've got salt buildups on the front, and they've got salt on the floor. So, it's a messy process, and we're talking about something almost purely caustic. So, some risks are involved, but as far as being scary technology, it's not. It's not intimidating to run, operate, or maintain well. So that's kind of what I want to talk about today. As scary as it will be physically, if you are just conscious of the risks, have good housekeeping, and maintain the tank, then it's an easy process to operate.
"There are only two things you need to understand to control the tank. And that's, ‘Am I boiling at the right temperature?’ And ‘Am I controlling my sludge content?’"
TP: And it's much needed. I know it's used in many fasteners, weaponry, and other things. It's a really good finish. It does the job that people want it to do.
JG: Yeah, it's weird because it kind of walks a line. It's a functional coating, and it needs a top coat to be a fully functional coding, but it falls into a lot of industries for decorative purposes, even though it's not really the intention. But, like you mentioned, a lot of fasteners and firearm stuff.
TP: Let's talk about the boiling point because that seems to be what many people get a little queasy about. Like you said, they don't like having a cauldron of hot liquid sitting around. Bad things often happen when that's the case. What is the boiling point, what's it telling you, and how do you interpret that?
JG: So, black oxide 101, there are only two things you need to understand to control the tank. And that's, ‘Am I boiling at the right temperature?’ And ‘Am I controlling my sludge content?’ And if you're on top of that, you shouldn't have many problems. Everyone always has cleaning problems and whatnot, but the bath is all you need. So, there's no titration you can do in the lab, really, that'll give you a great picture of the bath's concentration. Really, in the field or at the tank, the best thing you can do is just check the boiling point. The chemistry is designed to boil around 285°, and if you're gently rolling, boiling at 285°, you have enough salt in the tank, and that's it. Adding salt to water raises the boiling point, so you'll either add salt or water accordingly to ensure you're around that 285°, and you should be good to go.
TP: Let's talk sludge control. Let's talk about that. It's not something you normally hear in plating. Take a second; what exactly does that mean, and what is that process for the sludge?
JG: Sludge is the wild card. You don't have to deal with it with most plating processes, and I guess we'll take a step back. So black oxide is a conversion coating; it's not necessarily a plating process, even in plating shops. It's not this additive thing that you can keep building over time. You're dissolving this base layer and depositing this oxide crystal on it, and that's it. It's kind of like a cousin to rust. It's called magnetite, and it's a crystal. I think it's Fe304 off the top of my head and is a less stable form of rust. So, over time, it will rust and turn into your normal red oxide, but that dissolved iron kind of has to go somewhere. So, we're looking at this cauldron, as you put it.
Since we're boiling, we got a lot of solution movement. We're bringing a lot of hot sodium hydroxide to the surface. That will react with a lot of carbon dioxide in the air, where this sodium carbonate is formed. So now I've got sodium carbonate, I've got... We call it colloidal iron, that ironing solution. It's a cool word. It sounds fancy, but it just means kind of moving around, not doing anything, and that's kind of smashing up with that carbonate, and that together is falling out at that sludge. So that's what's on the bottom. There's usually some floating on top, we call that scum or scuzz. And then there's usually... You'll see the salt forming on the top of the tank, like a cocktail or something.
TP: Do you see a lot of finishers doing black oxide? Some have mentioned it, and it's funny because a couple of people I know, a couple of industry people that say they do black oxide, they don't do it. They say, "Well, we tell our people we do it, but we ship it out to somebody else to do it." But give me, percentage-wise, how many people and how many shops are doing this type of operation of black oxide.
My mentor always preached that "the chemistry's not smart enough to do that, so something else has to be going on. The chemistry can't pick and choose what it wants to blacken."
JG: So, plating shops that happen to have a black oxide process, you're right; it's pretty low. Around here, it's probably 5%, or 10%, if even. It is normally a dedicated shop, and there are quite a few of those smaller ones around here, and that's it. They have two or three black oxide lines and plenty of work to keep themselves staffed and busy. They're normally slammed. Black oxide, like I said, it's easy to control. It's a very simple process. It's not that sophisticated. So, we're talking about high-volume work, barrels, and racking. There are a lot of captive shops that do black oxide. We mentioned firearms. It's very big there. Almost every major gun manufacturer has their black oxide line internally. Then they also have a host of three or four local shops who have to help with the overflow, all the little components, and maybe people who specialize in different base materials.
TP: I know a couple in Chicago; they're running constantly. That's all they do, and they do it very well. They have very large tanks, but they're bustling. I mean, it's a lot of work they're getting because I think many people just decide not to get into it.
JG: It's hard to break into as well because it's more of a low-margin process, like the money is in the volume, so it's hard to start up and try to get competitive in that kind of environment. You really can't specialize, you know?
TP: What are some common quality issues you see some shops having with this, with their black oxide line, and how are they fixing it? What seem to be some things that crop up?
JG: Back to the sludge control we were talking about. So, that sludge has fallen off, and much is settling on the bottom. Most tanks in this industry are gas under fire. You do see some electrical heaters here and there, but you get all this falling off, and it will grow in the bottom. It's going to get denser, and quality issues stem from that. I remember a few years ago, I was at a gun customer, and they were running these vertical gun barrels, and I took the phone call. It started with a call, and he said, "Yeah, we're coming out of the tank, and the top third of every barrel is gray, and we don't know why the tank's doing this." So, my mentor always preached that "the chemistry's not smart enough to do that, so something else has to be going on. The chemistry can't pick and choose what it wants to blacken." So, we took a trip out there, and we were looking at the sludge, and it had just grown to a point, from poor maintenance, that the top third of the gun barrel was sitting in the sludge, so it wasn't seeing any fresh solution. Equipment blackened. So, de-sludging is part of a normal protocol. There are a couple of different ways to approach it, but the most effective way is to get in there if you're slightly below operating temperature and have some kind of equipment to just scoop it out. If your tanks are set up properly, you can decant the liquid on top, and then you could get in the tank and get the sludge out. But if you let it grow and grow and grow, it will start to touch parts, and then you run into some safety concerns at that point, too. One of the big things, I want to say boogeyman terms, is an eruption, but one of the bad things that can happen in a black oxide process. And it's exactly what it sounds like. And what happens is, if you're not de-sludging properly, if you're letting things go too far, that sludge will get thick on the bottom, and if any liquid gets under that, it can superheat from those gas under fire heaters. It's going to have to go somewhere eventually. It'll break through the sludge; you'll get a solution kind of burp up. You'll see it on the walls, on some ceilings. I mean, it's not funny. It can be kind of scary, but it's also easily preventable if you just stay on top of your housekeeping.
TP: Talk about housekeeping. What are they doing? When should they be de-sludging or whatever it is you're talking about? When should that be happening?
JG: It's all based on volume. You can start with a calendar and then dial it in from there. Some shops need to do it once a year; some need to do it every six months. Some of our super high-volume gun captive shops are doing it every other month. Those guys are set up for it, so they can do a really effective job. But even just the minimal, having some kind of tool on hand, and at the end of the week, you scoop some out the bottom, that'll keep you in great shape for a long time. It'll keep that colloidal iron from building and that sludge blanket from building. The other thing that can happen is if you wait too long and get too much of that iron in solution, you'll see the bath itself start to turn red, and your parts will start to turn red. And at that point, you can't fix the parts. Well, you can strip and re-black oxide, but you have to get the iron out of the bath at that point, or you're too far gone and just have to dump it and start from scratch.
TP: What are some of the black oxide products you all have? What do they do? What do they specialize in?
JG: For the hot black, just the baseline flagship product, that's just for normal steel, right? General steel processing. You do need a separate chemistry if you want to blacken stainless steel. It runs at a different temperature range; the package is slightly different. We have some black oxides for copper, copper-based alloys, brass, and that kind of stuff. And those need completely different technology. They run at different temperature ranges, they need some different pretreatment to get the black, and then there's also the cold blacks on the market. There are a bunch of different room temperature options available.
Black oxide is cool because there's not much you can do with it, but what you do to the metal beforehand will greatly impact the final coating.
TP: When you say cold black, are you talking about it not being heated?
JG: Yes, or if it is heated, it's minimal heat. Those cold blacks are room-temperature blacks. They're not a traditional black oxide, so you won't see any more popular functional applications using those because it's not that magnetite crystal. It's more of just a coloring. It's not the same functional coating. So, they're almost completely different technologies, even though they get a lot of umbrella-ed together. And you do see a lot of people asking like, "Oh hey, we can save a lot of energy by switching to one of these cold blacks," but it's not going to meet the same topological considerations.
TP: Like you mentioned, oxide one, what I noted when I visited out in Prescott, Arizona at the Ruger plant, and a lot of those, I remember them telling me that people are looking at these finishes who have a handgun or a firearm as works of art. I mean, they're really looking at those, so it's hard to get that right because you're going to have people looking at it more of as a decorative finish than a functional finish.
JG: Some of the gun industry run at slightly different parameters, too, just because they take it a little more seriously. They used to run... Many of the traditional gun industry would run two different black tanks because they felt it gave them this deeper shade of black. You don't see that too much anymore, but they tend to run longer immersion times just for that confidence level. Some people do say that you see a little bit of difference. I'm not a quality guy, and my eyes are not good. For the most part, the surface is converted in 15 minutes to half an hour, and you should be good to go. But you do see a lot of them looking for that jewelry finish. They'll go more than 45 minutes for more depth.
TP: What's the most interesting thing you've ever seen with black oxide on it? Does anything come to mind?
JG: I have been involved in some pretty cool firearms-related events. They've tried some special finishes. Black oxide is cool because there's not much you can do with it, but what you do to the metal beforehand will greatly impact the final coating. So, seeing people play around with different matte finishes and high gloss applications, we can get different colors coming up the back end. Depending on how you polish it, you can almost get some shades of blue.
